MKS Baratron 622D, Руководство пользователя

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Hysteresis of Type 623H Trip Relays Chapter Four: Operation
38
The noise in a system can cause the
pressure signal to vary back and forth
across an alarm trip point, causing the
relay to repeatedly change state. This
condition is known as relay chatter.
By incorporating hysteresis in the control
loop, relay chatter can be eliminated. If
the hysteresis is too great, however, a
deadband develops where changes in the
pressure signal around the trip point do not
trigger a change of relay state.
To avoid the inaccuracy which results from
too much hysteresis, the hysteresis may be
reduced. Too little hysteresis, however,
may not be enough to overcome relay
chatter.
Ideally, the hysteresis should be as close
to, but no less than, the peak-to-peak noise.
This setting will provide maximum
immunity from relay chatter while
providing the best possible accuracy.
Figure 9: How Hysteresis Affects Accuracy and Relay Chatter
Noise
Pressure
Relay State
Energized
De-energized
0 F.S.
Noise
Dead band
Pressure
0 F.S.
Relay State
Energized
De-energized
Overlapping
peak-to-peak
noise
Pressure
0 F.S.
Relay State
Energized
De-energized
Hysteresis
Peak-to-peak
noise level
Pressure
0 F.S.
Relay State
Energized
De-energized